Low-Resistance Ohmic Contacts to P-Inas for High-Speed Device Applications

Evaluation of five different metallizations schemes for ohmic contact to p-type InAs was performed. The metallizations evaluated were Ti/Pt/Au, W/Ti/Au, Mo/Au, Cr/Au and Pd/Pt/Au. All the metals except W were deposited by electron beam evaporation; W was deposited by both sputtering and evaporation. Four different samples of InAs were used for this study. Contact resistance was measured using the transmission line method (TLM) with a Kelvin probe connection to minimize measurement error. Exploratory studies of the feasibility of reducing contact resistance through temperature annealing, as well as increasing the surface acceptor concentration through post-growth doping were undertaken. Most of the contacts showed improvement in the contact quality (as manifested by the specific contact resistance) with annealing. Ti/Pt/Au contacts exhibited the lowest contact resistance of 2 X 10^{-7} Omega mbox{cm}^{2}$ after annealing at $200 ^{o}$C for 5 minutes. A spin-on glass source was used with rapid thermal diffusion to introduce Zn acceptors into the InAs. Contrary to simple contact models, this process resulted in increased contact resistance.